Ben - best thing is reformat your PC and install XP into it. Get a crack too so that you can get service pack 1.
i assumed that you are running a pentium something right?
Operating System... Win98, 2000, XP?
go to start -> program ... see if you have this software called 'GAIN'... if you do, get rid of it. Its an advertising software, including popups. It installs itself into your comp unknowingly.